The present invention relates to a golf ball having excellent flight performance.
Golf balls are provided on the surface with numerous planar circular depressions or dimples, in order to enhance their aerodynamic properties. It is well-known that, other factors being equal, golf balls with dimples fly better than golf balls which are smooth and have no dimples.
The distance traveled by a golf ball when hit with a golf club is determined by a number of factors, including the initial velocity of the ball, the drag and lift which act on the ball during its flight, the ball""s spin rate, and also weather conditions, all of which complicate theoretical analyses aimed at increasing the flight distance.
A great deal of effort has been devoted to maximizing the effects by dimples associated with the shape parameters of a golf ball on enhancing the ball""s flight characteristics, save for the initial velocity which is largely governed by the materials making up the ball. Innovations have included increasing the dimple diameter, using several types of dimples of differing diameter and thus size, increasing or reducing the dimple depth, and employing dimples of various planar shapes, ranging from circular to polygonal. Innovations relating specifically to the cross-sectional shape of the dimples have included round shapes (i.e., shapes representing the arc of a circle), composite shapes formed at by the superposition of a large and a small dimple, flat-bottomed shapes, and conical shapes. In addition, much experimentation has been done with the number of dimples on the ball""s surface. Such efforts have achieved a certain degree of success.
The use in golf balls of dimples having the various above shapes has been subject to aesthetic constraints associated with the ball""s appearance. Use is generally made of one type of dimple having a planar shape that is circular. Alternatively, where it is necessary to distribute the dimples over the ball""s surface in a uniform and tight arrangement, several types of circular dimples of different diameter are used. In the latter case, although the dimples are of different diameter, their cross-sectional shapes are substantially similar.
However, because such innovations have yet to provide golf balls with a flight performance that matches the high expectations and skill level of professional golfers and other advanced players, there exists a desire for further development and improvement.
It is therefore an object of the invention to provide a golf ball in which the aerodynamic properties are improved by arraying, over the ball""s surface, a combination of different types of dimples such as to impart the ball with a more complex surface geometry.
To attain this object, the invention provides a golf ball defining a substantially spherical surface on which a plurality of dimples are formed, each having a planar shape that is circular and a cross-sectional shape perpendicular thereto. The dimples are of at least three types including dimples of first, second and third types having small, medium and large diameters, respectively, in the planar circle. At least one of the at least three types of dimples has a cross-sectional shape differing from that of the other types of dimples. Such a golf ball, with its optimized dimple shape and optimized trajectory, has dramatically improved flight characteristics that enable it to satisfy the flight performance needs of even highly skilled golfers such as professionals. Moreover, the dimples on the inventive ball meet aesthetic requirements relating to the ball""s appearance because they are all circular in shape.
Typically, each type of dimple has a different cross-sectional shape. According to a preferred embodiment of the invention, one type of dimple has a cross-sectional shape defined by the union, in a cross-sectional plane, of at least two concave portions of differing slope which meet at a point of inflection located at a position preferably at least half as deep as the maximum depth of the dimple.
There may be cases where, in trying to give the golf ball a more complex surface geometry by conferring one type of dimple with a cross-sectional shape differing from that of the other dimple types, such differentiation in the cross-sectional shape fails to have the desired effect. However, the inventor has found that such differences in the dimple cross-sectional shape are indeed effective if they are in accordance with another preferred embodiment of the invention, wherein the dimples of at least one type have a value TVo which differs by at least 0.03 from the TVo values for the other types of dimples. Herein, TVo is defined by the equation:
TVo=Vo/(0.058 DM+0.677)
wherein Vo is the volume of space in the dimple below a planar surface circumscribed by the edge of the dimple divided by the volume of a cylinder whose base is the planar surface and whose height is the maximum depth of the dimple from the base, and DM is the diameter in millimeters of the planar surface circumscribed by the edge of the dimple (referred to herein as the xe2x80x9cdimple diameterxe2x80x9d).
Preferably the golf ball of the invention has no great circle on the surface thereof which does not intersect with a dimple.